PROJECT SUMMARY The mammalian female reproductive tract, including the oviducts, uterus, and vagina, is essential for the generation of progeny and a frequent site of human disease, including infertility and cancer. The female reproductive tract is derived from the Mllerian ducts (MD) of the fetus, a pair of epithelial tubes with a surrounding mesenchyme. In mammals, two pairs of genital ducts form within the mesonephroi associated with the fetal gonads regardless of sex genotype. Initially, the Wolffian ducts form that subsequently give rise to the vas deferentia, epididymides, and seminal vesicles in males. The Wolffian ducts then guide the formation of the MD that can form the oviducts, uterus, and upper vagina. The cell behaviors that regulate the elongation of the MD are poorly understood. We will use fluorescent, time-lapse imaging of the mesonephros to determine the cell behaviors and mechanisms that lead to MD elongation. We have shown that deletion of Lhx1, that encodes a LIM-homeodomain transcription factor in the MD, leads to ductal loss and uterine aplasia. In the absence of the MD epithelial compartment, the stroma and inner myometrial layer of the uterus do not differentiate. However, the outer myometrium forms. These results highlight the intrinsic and extrinsic roles of the MD for female reproductive tract differentiation. We will define the transcription factors that are expressed in the developing MD by RNA-seq and test their roles in uterine development by performing MD-specific knockouts. We will also describe the chromatin landscape of MD epithelial cells by ATAC-seq to identify candidate regulatory elements that will be tested in vivo. In males, the fetal testes produce the TGF-beta family member anti-Mllerian hormone (AMH) that binds receptors expressed in the MD mesenchyme, causing the elimination of the MDs. The fetal ovaries do not produce AMH, permitting MD differentiation. Thus, mammalian fetuses are initially ambi-sexual with the potential to develop both male and female reproductive tract organs. Defects in the formation of the genital ducts and resolution of the ambi-sexual state to a male or female phenotype lead to disorders of sexual development (DSD). RNA-seq of purified male and female MD mesenchyme identified AMH-induced candidate genes for MD regression. We will test their roles by performing MD mesenchyme-specific knockouts. ATAC-seq will also be performed to identify candidate regulatory elements that will be tested in vivo. Our goal is to define the gene regulatory networks that regulate female reproductive tract organogenesis and MD regression during male differentiation.